If you guessed # 3, you are correct.
The lethal dosage for a 150 pound adult is 60 mg. The lethal dosage for # 2 is 75 mg
and the lethal dosage for # 1 is 200 mg. In other words, nicotine is three times
as toxic as arsenic and one and one half times as toxic as strychnine.

Nicotine - a poisonous volatile
alkaloid, derived from tobacco and responsible for many of the effects of
tobacco. It first stimulates (small doses) and depresses (large doses) at
autonomic ganglia and myoneural junctions. It is also used as an insecticide and
fumigant. (source: Black's Medical Dictionary,
thirty-fourth edition)

Recent research has
shown in fine detail how nicotine acts on the brain to produce a number of
behavioral effects. Of primary importance to its addictive nature are findings
that nicotine activates the brain circuitry that regulates feelings of pleasure,
the so-called reward pathways. A key brain chemical involved in mediating the
desire to consume drugs is the neurotransmitter dopamine, and research has shown
that nicotine increases the levels of dopamine in the reward circuits.
Nicotine's pharmacokinetic properties have been found also to enhance its abuse
potential. Cigarette smoking produces a rapid distribution of nicotine to the
brain, with drug levels peaking within 10 seconds of inhalation. The acute
effects of nicotine dissipate in a few minutes, causing the smoker to continue
dosing frequently throughout the day to maintain the drug's pleasurable effects
and prevent withdrawal.

What people frequently
do not realize is that the cigarette is a very efficient and highly
engineered drug-delivery system. By inhaling, the smoker can get
nicotine to the brain very rapidly with every puff. A typical smoker will take
10 puffs on a cigarette over a period of 5 minutes that the cigarette is lit.
Thus, a person who smokes about 1-1/2 packs (30 cigarettes) daily, gets 300
"hits" of nicotine to the brain each day. These factors contribute
considerably to nicotine's highly addictive nature.

Addiction-
dependence on a substance to the point that stopping is very difficult and
causes severe physical and mental reactions. Pattern of compulsive drug use characterized
by a continued craving for a substance and the need to use the substance for
effects other than pain relief.

Nicotine - one
of the most toxic and addicting of all drugs and it is toxic by all routes of
exposure including the intact skin. ....also used as a contact insecticidal. Lewis'
Dictionary of Toxicology